Method of applying a binder to a wetlaid fibrous web

ABSTRACT

FIBROUS WEBS ARE MADE BY BRINGING LOOSE SYNTHETIC, ORGANIC OR INORGANIC FIBERS, IN THE FORM OF A SUSPUNSION BUT WITHOUT A BINDER, ON TO A MOVING POROUS CARRIER, AND PASSING THE FIBERS THROUGH A BINDER DISPERSION ON THE SAME CARRIER IN COVERED CONDITION. PREFERABLY, THE FIBERS ARE SANDWICHED BETWEEN TWO POROUS BELTS AND SO RUN THROUGH A TANK CONTAINING DISPERSION.

April 23, 1974 A. P. L. HEIDWEILLER 3,306,405

METHOD OF APPLYING A BINDER TO A WET"LAID FIBROUS WLB Original FiledSept. 8. 1969 ATTCIRN EYS United States Patent Int. Cl. D21d 3/00 US.Cl. 162-186 8 Claims ABSTRACT OF THE DISCLOSURE Fibrous webs are made bybringing loose synthetic, organic or inorganic fibers, in the form of asuspension but without a binder, on to a moving porous carrier, andpassing the fibers through a binder dispersion on the same carrier incovered condition. Preferably, the fibers are sandwiched between twoporous belts and so run through a tank containing binder dispersion.

This is a continuation of application Ser. No. 856,118, filed Sept. 8,1969, now abandoned.

This invention relates to a method of, and apparatus for, producingfibrous webs, which comprises bringing loose synthetic organic orinorganic fibers, or mixtures thereof in the form of a suspension inwater or in a watermiscible solvent on a porous, moving carrier,providing the fibers with a binder, removing the Water or solvent fromthe carrier, and drying the resulting moist fibrous web.

There are many known processes for producing fibrous webs by the wetmethod. In most cases, a homogeneous suspension ofsynthetic, organic, orinorganic fibers and the binder in water is applied to a porous carrier,the water is withdrawn by suction, followed by drying, whereafter thefibrous web thus formed is removed from the carrier. The disadvantage ofthis process is that a high percentage of the binder is withdrawn andremoved along with the water. Consequently, either the amount of binderwhich is left in the web is insufficient, or a large excess is used, inwhich latter case the great losses in binder represent a considerablecost item. Moreover, it is impossible to transfer the impregnated, Wetweb in a self-supporting manner from the carrier on which it isde-watered to a next carrier which carries the web through the dry ingand hardening furnace, since the webs coherence and strength areinsufficient for the purpose. To remedy this drawback, it would ofcourse be possible to carry out impregnation, drying and hardening onone and the same porous belt. This, however, has the drawback that whenthe carrier or belt becomes fouled with binder, this can no longer beremoved in a simple way after it has dried and hardened. In this wayvarious pores of the carrier become clogged. During the next cycle ofthe carrier no de-watering takes place at these clogged positions, sothat no fibers are deposited either. This results in thin spots or holesin the ready web.

3,806,405 Patented Apr. 23, 1974 ICC According to the invention, thefiber suspension is brought on to a moving, porous carrier without abinder, and passed through a binder dispersion on the same carrier incovered condition, whereafter the fiber suspension, soaked with binder,is freed of excess binder dispersion while still being on the samecarrier, and ultimately dried separately from the carrier in separatedrying apparatus.

The advantage of the subject method is that a homogeneous distributionof the binder throughout the fibers is ensured, without incurring therisk that the homogeneous layer of loose fibers is deformed, orinhomogeneities arise due to clogging of the pores of the carrier.

The fact that satisfactory fibrous webs can be produced in this way ismore or less surprising, because it was unexpectable that, withoutdrying and possibly hardening the binder, the web would be sutficientlyself-supporting for it to be taken over by the moving belt of the dryingapparatus without being damaged.

In a preferred embodiment of the invention, the carrier with the fibersuspension, into the binder dispersion in more or less tensionedconditioned around a roller while being covered with a belt passedbetween the roller and the layer of fibers. This belt need not be drivenseparately, but is adequately taken along by the moving carrier for itto run fully along with the latter.

Because of the fact that, in rounding the roller, the fiber suspensionor layer of fibers is compressed between the carrier and the belt, thequantity of water or solvent that may still be present is largelysqueezed out of the layer of fibers; since this compression is soonreleased again, the binder dispersion is subsequently absorbed into thesuspension or layer of fibers.

This embodiment has been found to be very satisfactory in practice. Thiswas by no means obvious, for the two belts necessarily have a differencein velocity in rounding the roller in the binder dispersion (owing tothe difference in length of trajectory) so that the suspension or layerof fibers between the belt is subjected to shearing forces.Unexpectedly, however, a web thus produced turned out to be extremelyfree of blemishes and of excellent strength.

Preferred organic synthetic fibers are polyamide and polyester fibers,but fibers of other kinds of polymers may be used. Suitable inorganicfibers are glass and asbestos fibers. In addition, mixtures of thefibers mentioned may be used.

The suspension medium for the fibers is preferably water, butwater-miscible solvents may be used. The same applies to the dispersingagent for the binder. Examples of organic solvents are ethylene glycol,propylene glycol, methyl and ethyl Cellosolve, as well as dimethylformamide.

As for the binder, any binder dispersible in water or in water-misciblesolvents, and which imparts sufiicient coherent strength to the webafter drying will be suFable for the purposes of the invention. If thebinder is soluble in the dispersing agent used, the binder dispersionshave the form of solutions, otherwise of emulsions or suspensions.Examples of soluble binders are: starch, starch derivatives, cellulosederivatives, phenolformaldehyde condensates, condensates of formaldehydewith amino compounds, polyamides, and many others, so long as they aresoluble in water or in water-miscible solvents. Examples of the binderemulsions are latices of elastomers, such as butadiene-styrenecopolymers.

If so desired, two or more binders may be used. In that case thesuspension or layer of fibers is passed through two or more binderdispersions, in covered condition in the manner indicated, withintermediate extraction between the stages.

The carrier may be made of the porous materials, which in paper makingmachines are used for the so-called copper cloth. Preferably a carrierof synthetic material is used. The covering belt is preferably made of asimilar porous material.

The diameter of the roller in the binder dispersion ranges from to 60cm. If the diameter is unduly large, the webs formed will showinhomogeneities, first of a minor nature, and later more marked.

Suitable apparatus for carryig out the method according to the inventioncomprises an endless porous belt running over a number of rollers, meansfor supplying the fiber suspension, a plurality of suction devices, oneor more tanks for binder dispersion including a substantially horizontalrotary roller therein, below which runs the belt carrying the fibersuspension or layer of fibers, a second belt running over a plurality ofrollers and passing between said rotary roller in the binder solutionand the first belt carrying the fiber suspension or layer of fibers, anda washing device which frees the first belt from residues of binder andfibers.

One embodiment of the apparatus according to the invention will :bedescribed by way of example with reference to the accompanyingdiagrammatic drawing, which shows a vertical, longitudinal view of theapparatus.

Referring to the drawing, 1 is an endless porous belt web or screen, forexample, as used in paper machines, passed over rollers 2, 3, 4 and 5. Adispenser for the fiber suspension is designated by 6, while 7 and 8represent suction devices for removing as much excess of water orsolvent and binder dispersion as possible. A belt or web 9 runs overrollers 10 and 11 and, just as the belt 1, under roller 12. in a tank 13filled with binder dispersion. Washing devices 14 and 15 are providedfor washing the two belts clean of binder.

In operation, the belt 1 rotates over rollers 2, 3, 4, 5, 16, 17 and,under a certain tension, around roller 12. At this latter point, thebelt 1 acts as a means for driving the belt 9, passed between the belt 1and the roller -12. A suspension of the desired fibers, for example,polyamide and/or glass fibers, is sprayed on to the belt 1 through thedispenser 6. This suspension is partly de-watered by the suction device7, for example, down to a dry content of about 40%. Then the uppersurface of the partly de-watered suspension, which at this point is notyet self-supporting, is contacted by the belt 9. The tripartiteassembly: belt 1,

the partly de-watered suspension, which has here adopted the characterof a layer of fibers, and the belt 9, next runs through the binderdispersion in the tank 13, around the roller 12, and back upwardly,where a suction device 8, provided with a small roller 16, provides forthe belt 1 and the binder-containing layer of fibers to be released fromthe belt 9. The belt 9 runs via roller 10, washing device 15, and roller11 back to the point where it comes again into contact with the partlyde-watered fiber suspension on the belt 1.

The belt 1 with the binder-containing layer of fibers is freed frombinder dispersion as much as possible by the suction device 8,whereafter the belt is passed via rollers 4 and 5, washing device 14,and rollers 2 and 3 back to the feeding device 6. The most web formedafter the passage of the suction device 8 is taken from the belt 1 inselfsupporting condition at the roller 4, and transported further by abelt 18 circulating through drying apparatus, in

which the web is heat treated to dryness and the binder is possiblyhardened.

In order that the squeezing and absorbing elfect occurring around theroller 12 be as great as possible, the downcomings and the rising partof the belt 9 are preferably disposed at an acute angle relative to eachother. A minimum value is 10, however. Also, it is recommendable thatthe two belts 1 and 9 are not firmly pressed together for the entirelength that they are in contact with each other. It is better to havethe two belts converge in the downcoming part from about 5 mm. topractically 0, and diverge in the rising part back to about 5 mm. Inthis way it is achieved that the binder is properly and highlyhomogeneously distributed over the fibers.

As defined in the claims the phrase in-going path portion refers to theportion 20 of the webs 1, 9, the phrase out-going path portion refers tothe portion 21 of the webs 1, 9, and the phrase apex path portion refersto the portion 22 of the webs 1, 9 partially entrained about the roller12. More specifically, the apex path portion is that portion of the Web9 from its first contact with the roller 12 to a point at which it losescontact with the roller 12.

The above apparatus affords continuous and undistributed production of afibrous web for a week or longer. The product is homogeneously providedwith binder, and shows no holes or other inhomogenieties even afteroperation for many days. The most widely dilferent kinds of fibers andbinders can be used. Finally, the apparatus is subject the minimum wear,because residues of binder are removed from the belts while still inmoist and/or unhardened condition.

I claim:

1. In a method of making fibrous Webs comprising the steps of admixinloose fibers in a liquid to form a suspen sion, depositing thesuspension on a moving porous carrier, conveying the liquid-fibersuspension along an acute angle path of travel defined by in-going andout-going path portions joined together by an apex path portion, saidapex path portion being immersed in a liquid binder, compressing theliquid-fiber suspension prior to its immersion into the liquid binderand during its immersion in the liquid binder while moving along saidin-going path portion at least to said apex path portion, reducing thecompression of the liquid-fiber suspension While moving along saidout-going path portion when both in and out of the liquid binder wherebythe liquid-fiber suspension is at least partially deliquified during itsmovement along the in-going path portion and the thereafter deliquifiedliquidfiber suspension expands during movement along the outgoing pathcreating a suction effect to draw thereinto the liquid binder, theimprovement comprising confining the liquid-fiber suspension betweenporous moving webs during the conveying thereof along said acute anglepath of travel, performing the compressing step by converging the websalong the in-going path portion, and later performing the reducing stepby diverging the webs during movement thereof along the out-going pathportion.

2. The method as defined in claim 1 including the step of partiallydewatering the liquid-fiber suspension prior to movement thereof alongsaid in-going path portion.

3. The method as defined in claim 1 wherein said apex path portion is inpart defined by a roller totally immersed in said liquid binder aboutwhich said webs are at least partially entrained.

4. The method as defined in claim 1 including the step of partiallydewatering the liquid-fiber suspension after movement thereof along saidout-going path portion.

5. The method as defined in claim 1 wherein one of said porous movingwebs is of a generally triangular configuration having two path,portions disposed at an angle corresponding to the acute angle definedby the ingoing and out-going path portions, and said last-mentioned webincludes another portion between said in-going and out-going pathportions remote from said apex path portion along which a cleaning stepis performed during the movement of the last-mentioned web.

6. The method as defined in claim 3 including the step of partiallydewatering the liquid fiber suspension prior to movement thereof alongsaid in-going path portion.

7. The method as defined in claim 3 including the step of partiallydewatering the liquid fiber suspension after movement thereof along saidout-going path portion.

8. The method as defined in claim 3 wherein one of said porous movingwebs is of a generally triangular configuration having two path portionsdisposed at an angle corresponding to the acute angle defined by thein-going and out-going path portions, and said last-mentioned webincludes another portion between said in-going and outgoing pathportions remote from said apex path portion along which a cleaning stepis performed during the movement of the last-mentioned web.

References Cited UNITED STATES PATENTS 7/1961 Krumsiek, Jr., et a1.

162165 X 2,104,052 '1/ 1938 Novak 162-265 ROBERT L. LINDSAY, 111.,Primary Examiner W. F. SMITH, Assistant Examiner US. Cl. X.R.

